This invention relates to arrays, particularly biopolymer arrays such as DNA arrays, which are useful in diagnostic, screening, gene expression analysis, and other applications.
Polynucleotide arrays (such as DNA or RNA arrays), are known and are used, for example, as diagnostic or screening tools. Such arrays include regions (sometimes referenced as spots or features) of usually different sequence polynucleotides arranged in a predetermined configuration on a substrate. The arrays, when exposed to a sample, will exhibit a binding pattern. This binding pattern can be observed, for example, by labeling all polynucleotide targets (for example, DNA) in the sample with a suitable label (such as a fluorescent compound), and accurately observing the fluorescent signal on the array. Assuming that the different sequence polynucleotides were correctly deposited in accordance with the predetermined configuration, then the observed binding pattern will be indicative of the presence and/or concentration of one or more polynucleotide components of the sample.
Biopolymer arrays can be fabricated using either in situ synthesis methods or deposition of the previously obtained biopolymers. The in situ synthesis methods include those described in U.S. Pat. No. 5,449,754 for synthesizing peptide arrays, as well as WO 98/41531 and the references cited therein for synthesizing polynucleotides (specifically, DNA). The deposition methods basically involve depositing biopolymers at predetermined locations on a substrate which are suitably activated such that the biopolymers can link thereto. Biopolymers of different sequence may be deposited at different regions of the substrate to yield the completed array. Washing or other additional steps may also be used. Procedures known in the art for deposition of polynucleotides, particularly DNA such as whole oligomers or cDNA, are described, for example, in U.S. Pat. No. 5,807,522 (touching drop dispensers to a substrate), and in PCT publications WO 95/25116 and WO 98/41531, and elsewhere (use of an ink jet type head to fire drops onto the substrate).
In array fabrication, the quantities of DNA available for the array are usually very small and expensive. Sample quantities available for testing are usually also very small and it is therefore desirable to simultaneously test the same sample against a large number of different probes on an array. These conditions require use of arrays with large numbers of very small, closely spaced spots. During use of an array, such as for gene expression monitoring or for patient testing, it will often be desirable to test very large numbers of such small samples against the many of the same or different array patterns. Thus, it is desirable to provide a convenient means by which many samples can be exposed to many arrays in a highly parallel process.
U.S. Pat. Nos. 5,874,219 and 5,545,531 provide a DNA chip wafer to which a plate carrying multiple channels can be mounted, to provide many test wells. Grace Bio-Labs, Inc., of Bend, Oreg., manufactures xe2x80x9cPerfusion Chambersxe2x80x9d which include covers with openings and which can be placed on specimen slides. However, the present invention appreciates that sample fluid loss can occur in chambers with openings, particularly as a result of evaporation under the elevated temperatures used over a number of hours during hybridizations of nucleic acid arrays. Such losses can potentially result in inaccurate results. Sample contamination may also occur through uncontrolled openings. Furthermore, it may be difficult to provide positive or negative pressure to the chambers to load or empty them while avoiding sample loss. The present invention recognizes that when chambers become very thin to accommodate small sample volumes, capillary forces become significant and some positive means of loading and/or emptying the chamber should preferably be provided which at the same time will avoid sample loss. As well, the present invention recognizes that any closed chamber system for arrays which uses assembled components should be provided with some way of avoiding pushing apart of chamber components as a result of internal pressure increases during heating.
As already mentioned, the testing of multiple samples on multiple arrays on a single substrate has potential to expedite and simplify multiple sample handling. However, such a technique also has the potential to propagate multiple errors. For example, in the case of hybridizing multiple samples to a contiguous substrate carrying multiple polynucleotide arrays, elevated temperatures over a lengthy predetermined time may be required. If for any reason inadequate conditions were provided (for example, by failure of a heating system to reach and maintain the required temperature for the required time), poor results may be obtained. It has been previously disclosed to use control oligonucleotide probes and reference nucleic acid sequences with single arrays. The reference sequences are mixed with sample and the mixture exposed to the array. Hybridization of reference sequences to corresponding reference features, is used as an indication of overall assay performance. However, since sample is present together with reference sequences, there is a potential of interference from similar sequences in a sample. In a conventional situation, where a single sample is tested on a single array, and the inadequate hybridization conditions are not detected, this might lead to a single error. However, with a single substrate carrying multiple arrays, this might suggest system failure and lead to invalidating multiple test results, when the error may in fact be due to interference of the test sample on the hybridization of the reference target to the reference features.
The present invention realizes that it would be desirable then, to provide apparatus and methods for testing multiple samples with multiple arrays, particularly biopolymer arrays such as DNA or RNA arrays, which retain the samples in readily accessible chambers and yet which will not likely suffer sample loss or contamination. The present invention further realizes that it would be desirable that an apparatus and/or method for testing multiple samples with multiple biopolymer arrays, should preferably be able to provide features which include one or more of the following: the ability to allow samples to be positively loaded into or withdrawn from the chamber while avoiding sample leakage; tolerance for increased temperatures without adverse sample loss; of relatively simple constructions; be easy to clean and preferably with any components subject to wear being readily replaceable; and the ability to avoid multiple undetected errors.
The present invention then, provides in one aspect a method of testing multiple fluid samples with multiple biopolymer arrays. This, or any other aspects of the method, may use any suitable apparatus as described herein. Any of the fluid samples may be of the same or different compositions. The method includes assembling a cover to a contiguous substrate which carries on a first side, multiple arrays each with multiple regions of biopolymers linked to the substrate. As a result, the cover and the substrate together form a plurality of chambers each containing a biopolymer array and each being accessible through its own port. The method further optionally includes introducing multiple fluid samples into respective chambers through a port of each such that the fluid samples contact respective arrays, and observing the binding pattern of the arrays. The binding pattern may be observed in any suitable manner, whether directly or indirectly.
The method may particularly use an apparatus in which each chamber is accessible through a first and a second port. In this case, fluid samples may be introduced into respective chambers through respective first ports while venting through respective second ports. This introduction of multiple fluid samples may optionally be performed simultaneously. The ports may include a resilient self-sealing portion. In this case, the method may additionally include inserting a first set of conduits through the resilient members of respective first ports, and inserting a second set of conduits through the self-sealing portion of respective second ports, with the multiple fluid samples being introduced into each chamber through the first set of conduits while venting occurs through the second set of conduits.
The assembling step of the method may include applying an external force to urge the cover toward the substrate and which remains applied to retain them in the assembled position. By xe2x80x9cremains appliedxe2x80x9d in this context refers to at least remaining applied for one or ten minutes, or at least an hour or multiple hours, and typically refers to remaining applied during manipulations during and following loading of the chambers with samples (for example, including the period following loading during which the temperature may be raised). While many ways of applying and retaining such pressure are possible, a coupler may be used which extends between the cover and the substrate to urge the cover toward the substrate and retain them in the assembled position. The coupler used may be of various configurations, and in one configuration includes a plate with at least one view opening as well as an adjustable interconnect member. With this configuration, the coupler application includes positioning the plate facing a second side of the substrate with the at least one view opening in alignment with the arrays such that the arrays can be observed from the second side of the substrate through the at least one plate view opening. The adjustable interconnect member is extended between the cover and the plate, and adjusted to urge the cover toward the substrate.
In a second aspect of the method of the present invention, a cover is used which includes a cover member and a resilient gasket with multiple openings. These are assembled to a substrate as described above, with the gasket sandwiched between the substrate and cover member and the gasket openings aligned with respective array, such that the cover, substrate, and gasket together form a plurality of chambers. Each of the chambers contains a biopolymer array and is accessible through a port comprising respective port portions of the resilient gasket which normally close the port. The method optionally includes penetrating gasket port portions by at least one conduit and introducing fluid samples into respective chambers through the at least one conduit, such that the fluid samples contact respective arrays. A binding pattern of the arrays may then be observed.
In the second aspect, following assembly the gasket may have a first side facing the substrate and a second side facing the cover member, as well as port portions positioned transversely beyond the substrate. In this configuration, the ports may further include respective fluid ducts in the cover member communicating between respective chambers and respective port portions of the gasket. With this arrangement, the chambers can be accessed by conduits which have penetrated from the first side of the gasket through the port portions to the ducts. The ducts in the second aspect may be of various structures and may, for example, be channels in a first side of the cover member which faces the gasket. Each chamber may again have a first and a second port. The gasket port portions then, act as the resilient self-sealing port portions described above, and can receive conduits therethrough to provide fluid samples and venting in a similar manner as already described. A coupler may be applied between the cover and the substrate, of the same construction and in the same manner as already described.
A third aspect of the methods of the present invention provides a method of testing multiple fluid samples using a contiguous substrate carrying multiple arrays each with multiple regions of biopolymers linked to the substrate. At least one array of the substrate is exposed to a test sample (and optionally, also to a reference sample) under a first set of conditions, and at least one other array is exposed to a reference sample under the same set of conditions. The at least one other array is not exposed to a test sample. This aspect may also include observing a binding pattern of the arrays and, when an observed characteristic of the binding pattern of an array exposed to the reference sample is outside a predetermined limit, either rejecting the binding pattern result for the test sample or modifying observed binding pattern results for the test sample based on a difference between an expected and observed characteristic of an array exposed to the reference sample. Typically (which implies not necessarily) multiple test samples may be exposed to respective arrays. All exposing may or may not be simultaneous. This aspect may optionally further include assembling the cover to the first side of the substrate on which the arrays are carried, such that the cover and the substrate together form a plurality of chambers each containing a biopolymer array and each being accessible through its own port. The multiple test samples and reference sample may be introduced (for example, simultaneously), into respective chambers through a port of each such that the fluid samples contact respective arrays. The binding pattern of the arrays may then be observed. This aspect may optionally further use any of the steps of the other aspects of the methods of the present invention. It will also be appreciated that any additional steps considered desirable, may be used in any aspects of the present method. For example, the methods may optionally additionally include, after applying the coupler, heating the chambers.
In another method of the present invention, the array exposed to the test sample and the array exposed to the reference sample both include at least one reference feature, and wherein both are exposed to at least one reference sequence. These common reference features may, for example, be identical. Similarly, the reference sequence or sequences for each may, for example, also be identical. Again, the binding pattern of the arrays is observed as before. When the binding patterns of the at least one reference feature in both arrays lack a predetermined degree of correlation, the binding pattern result for the test sample is either rejected or an observed binding pattern result for the test sample is modified based on a difference between an expected and observed correlation. In the case of identical reference features in both arrays and the same reference sequence or sequences exposed to each, the predetermined degree of correlation may simply be the predetermined degree of similarity in observed binding at the reference features of both such arrays.
The present invention further provides apparatus of the type which may be used in methods of the present invention. In one aspect, such an apparatus includes a cover defining multiple cavities on a first side and with respective ports communicating with the cavities. The ports include respective resilient self-sealing portions normally closing the ports. The cover can be assembled to a contiguous planar substrate carrying on a first side, multiple arrays each with multiple regions of biopolymers linked to the substrate, such that the cover and the substrate together form a plurality of chambers each containing a biopolymer array and each being accessible through its own port.
The apparatus may optionally further include the foregoing planar substrate attached to the cover, whether permanently (as by bonding with adhesive, welding, or some other means) or releasably (that is, not bonded thereto). In an aspect of the apparatus using a gasket, the gasket may or may not be one which is not adhered to the cover member such that following detachment of the cover from the substrate, the gasket freely detaches from the cover member. The gasket may be of various thickness and may, for example, be sufficiently thick as to define at least 50% (or at least 70% or 80%) of the maximum distance between a substrate and the cover member in the chambers. Also, while the cover member may be of various configurations, it may particularly be a unitary plate, and may further particularly be flat on a first side which faces the substrate when the cover is assembled thereto. By xe2x80x9cflatxe2x80x9d is meant substantially flat and allowing for irregularities such as the channels therein already described. The cover member may also have guide openings alignable with respective port portions of the gasket. Such a configuration allows the guide openings to facilitate the conduits correctly registering with the port portions of the gasket. While the chambers formed from the cover with a contiguous flat substrate may have various dimensions, the maximum distance between the substrate and the cover in the chambers, defined by the thickness of the gasket, may, for example be no greater than 5 mm (or no greater than 2 mm or 1 mm). The minimum thickness of the gasket may also be within virtually any desired range limited by properties of the material selected. For example, a minimum gasket thickness may be on the order of at least 0.75 mm (or even at least 0.5 mm). Further, the maximum volume of each of the chambers may, for example, be no more than 1000 xcexcl (or even no more than 500 xcexcl, 200 xcexcl or 100 xcexcl), and may typically be 20 to 200 xcexcl.
The present invention also provides in a further aspect, a kit for testing multiple fluid samples, comprising a contiguous substrate carrying multiple arrays each with multiple regions of biopolymers linked to the substrate, and a reference sample for exposure to at least one of the arrays. Such a kit may optionally include an instruction that the reference sample is for reference. This instruction may, for example, be in printed, human readable characters on a suitable medium (such as a label adhered to container carrying the reference sample). For example, the instruction might simply be printed as xe2x80x9cREFERENCExe2x80x9d, xe2x80x9cREFxe2x80x9d or similar. However, the instructions may include further instructions such that the reference sample is to be exposed to at least one array, or that the reference sample is to be exposed to at least one array under the same set of conditions as at least one test sample being exposed to another array on the same substrate. The kit may, if desired, further include a contiguous substrate carrying multiple arrays each with multiple regions of biopolymers linked to the substrate, and comprising a gasket with multiple openings which are alignable with respective arrays on the substrate.
While the substrates in the aspects of the apparatus, methods and kits of the present invention described above, carry biopolymers, the present invention contemplates that these particular moieties can readily be replaced with other moieties (such as other chemical or biochemical moieties, for example various small molecules) in any of the apparatus, methods or kits of the present invention. Thus, wherever a reference is made to biopolymers, this can be replaced with any such moieties. It will also be appreciated that any of the arrays described, may be the same or different (although often multiple ones, if not all, of the arrays on a substrate will be the same), and may or may not be separated by an intervening space. If there is no intervening space, the gasket may simply cover some areas of biopolymers (which then simply go unused). However, typically the arrays are distinguishable from each other in some manner, such as by an intervening space or by the patterns of the moieties thereon.
The method, apparatus, and kits of the present invention can provide any one or more of a number of useful benefits. For example, the samples exposed to arrays are retained in closed yet readily accessible chambers. Samples can be positively loaded into chambers containing and withdrawn therefrom, under the influence of a slight pressure or vacuum (such as from a syringe) while avoiding sample leakage. Increased temperatures can be well tolerated without generating pressures which could push apparatus components apart and lead to sample loss. The apparatus is relatively simple to construct and, if desired, easy to clean. Components of the apparatus which are particularly subject to wear, such as the resilient gasket at the port portions, is readily replaced while allowing the remainder of the apparatus to be re-used many more times. Further, where a gasket is used chamber volume can be readily altered by using a different gasket. In the case of aspects utilizing a reference, this allows for easy monitoring of error conditions.